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I think i need some type of MockUp to be sure.
And even then its NEVER going to be 100% sure that it will be safe.
Products go through rigorous testing before they can say WITH ANY CERTAINTY, that a product has a weight limit.
So unless you plan on doing stress testing, there will never be any way to know.
However, reinforcing all THE JOINTS, and adding in some structural bracing, should keep the additional weight at bay.
Although, and again.....there will NEVER be a 100% sure thing....unless you TEST it under lab conditions.